Re: [time-nuts] Four hour cycle in GPS NMEA jitter

On Thu, 2017-03-23 at 08:28 +1300, Kiwi Geoff wrote: > On 3/22/17, Trent wrote: > > https://goo.gl/photos/JZhBbFKFzkBAykti6 > > Why would a GPS module produce jitter with a pattern like this? > > Trent, I decided to R.T.F.M.(read the fantastic manual ;-) > > It looks like that in your Telit

Re: [time-nuts] Four hour cycle in GPS NMEA jitter

On 3/22/17, Trent wrote: > https://goo.gl/photos/JZhBbFKFzkBAykti6 > Why would a GPS module produce jitter with a pattern like this? Trent, I decided to R.T.F.M.(read the fantastic manual ;-) It looks like that in your Telit module, there is a mode called

[time-nuts] Four hour cycle in GPS NMEA jitter

I did a lot of work in Lady Heather to add timing message arrival time analysis capability. Heather has a "set the system clock to receiver time" function that is intended to be used on systems without access to something like NTP. By knowing the arrival time of the last byte of the timing

Re: [time-nuts] Four hour cycle in GPS NMEA jitter

> https://goo.gl/photos/JZhBbFKFzkBAykti6 > Why would a GPS module produce jitter with a pattern like this? Trent, I must admit I have not seen such a four hour "spike" before in the NMEA latency, however a clue may be that the GPS ephemeris (broadcast by the SV's) orbit description is valid only

Re: [time-nuts] Four hour cycle in GPS NMEA jitter

HI > On Mar 21, 2017, at 4:52 PM, Trent Piepho wrote: > > Thanks to all who responded. Yes, I know PPS is the way get a more > accurate timestamps. That is the plan, but it takes more time to write > FPGA programs. The surprise is not that there is considerable

Re: [time-nuts] Four hour cycle in GPS NMEA jitter

Wow. 350 nS. I had not been following this for the last few years. It seems the ARM is a simply CPU with much more predictable interrupts timing. One might ask way you'd need such good internal timing. What got me into this years ago was scientific data acquisition. I wanted to time

Re: [time-nuts] Four hour cycle in GPS NMEA jitter

Yo Chris! On Mon, 20 Mar 2017 15:19:25 -0700 Chris Albertson wrote: > I've only hear of 1 uS being broken with hardware. A Raspberry Pi can get down to a Standard Deviation of about 350 nano seconds using NTPsec.. https://blog.ntpsec.org/2017/02/01/heat-it-up.html

Re: [time-nuts] Four hour cycle in GPS NMEA jitter

Hi Trent, > But first things first. I'm just grabbing the time from NMEA sentences. > And there's quite a bit of jitter there! Clearly using the first sentence > output by the GPS is critical. I've tried to account for any time delays in > the software. I think it's the GPS module that is

Re: [time-nuts] Four hour cycle in GPS NMEA jitter

Hi NMEA sentences are not the best thing to use for timing. If you *do* decide to use them, configure the receiver so that one and only one sentence comes out. Any time you have more than one, you run the risk of collision in the serial buffer on the part. Next thing to do is to pick the

Re: [time-nuts] Four hour cycle in GPS NMEA jitter

> Does this sound like something that one would expect with the NMEA output of > a non-timing GPS? Is it related to satellite orbits? Or perhaps is has > something to do with the design of the SiRFStar IV? > Remember the phone based time service? "At the tome time time will be BEEP"

[time-nuts] Four hour cycle in GPS NMEA jitter

Hello time nuts, I'm working on a custom embedded Linux device, with a custom inertial reference unit, which contains a GPS module. The module is a Telit JN3, which is based on the SiRFSTAR IV I believe. I'd like to use the GPS to sync the Linux system clock. Eventually I'd like to use the